JP4719551B2 - Charging condition adjusting method for charging device, and image forming apparatus and image forming process cartridge using the charging condition adjusting method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a fax machine, or a multifunction machine having these functions, and a process cartridge, and more particularly between a photosensitive member ( image carrier ) and a charging roller for efficient charging. This relates to an adjustment method for determining the optimum gap and the like . The process cartridge refers to a cartridge in which at least the photosensitive member and the charging unit are integrated into a cartridge that can be attached to and detached from the image forming apparatus main body.

JP 2004-264792 A JP 2002-108059 A JP-A-2005-4000

  In an image forming apparatus using an electrophotographic process, image formation is performed by subjecting a photoreceptor to a charging step, an exposure step, a development step, a transfer step, and a fixing step. For the charging process, scorotron chargers have been used in the past. However, due to environmental problems, generation of harmful gases such as ozone and NOx is small, and a charging roller that can reduce the size of the device has recently been used as a charger. It is becoming. When image formation is performed while the charging roller is in contact with the photoconductor, if the residual toner after transfer cannot be completely cleaned, the residual toner adheres to the charging roller, causing variations in the resistance of the charging roller, and charging the photoconductor. As a result, the potential varies and causes uneven image density. Therefore, methods have been proposed in which a gap is provided between the photoconductor and the charging roller to charge the photoconductor (for example, Patent Document 1, Patent Document 2, and Patent Document 3). In this charging step, the photoconductor can be set to a target voltage by applying an alternating voltage in a superimposed manner. The charging parameters at this time include the AC voltage and frequency to be applied, the resistance (resistance unevenness) of the charging roller, the resistance of the photosensitive member (resistance unevenness), the gap between the photosensitive member and the charging roller, and the gap variation. The applied AC voltage determines the distance between the photosensitive member and the charging roller that can cause discharge. The larger the applied AC voltage, the more the discharge occurs even when the distance between the photosensitive member and the charging roller increases. be able to. For this reason, as the alternating voltage to be applied increases, discharge occurs in a wider area of the charging roller, so that the charging unevenness of the photoreceptor can be reduced. However, since discharging is a process in which charged particles such as ions and electrons are exposed to the photosensitive member and the charging roller, oxidation deterioration of the photosensitive member and the charging roller occurs. When the alternating voltage to be applied is large, the amount of generated charged particles and their energy increase particularly when the distance between the photosensitive member and the charging roller is small, so that the oxidative deterioration of the photosensitive member and the charging roller becomes severe. The charging roller must be replaced early. The applied AC frequency determines the number of times that discharge can occur per unit time. Therefore, the larger the applied AC frequency, the smaller the charging unevenness of the photoconductor. If the frequency is high, the photoconductor and the charging roller are oxidatively deteriorated, and the photoconductor and the charging roller must be replaced early.

  Further, if the distance between the photosensitive member and the charging roller is too close, no discharge will occur, and according to Paschen's law, no discharge will occur at about 7 μm or less. In reality, due to the electric capacity of the photoconductor and the resistance of the charging roller, it is said that the distance between the photoconductor and the charging roller where discharge starts to occur is approximately 20 μm or more. For this reason, it is very important to control the interval between the photosensitive member and the charging roller in units of μm. However, since the charging roller actually has a surface roughness of μm unit, there is no uneven charging of the photosensitive member. As described above, the value of the applied AC voltage and frequency is often set higher. The discharge between the photosensitive member and the charging roller has a high electric field strength at a distance (approximately 20 μm) between the photosensitive member and the charging roller where discharge can start to occur, and therefore the charged particle energy is high, and the photosensitive member and the charging roller are oxidized and deteriorated. Will be intense. Therefore, if the distance between the photosensitive member and the charging roller is sufficiently large, the oxidative deterioration of the photosensitive member and the charging roller can be suppressed. However, if the distance is too large, the discharge varies and the applied AC voltage and frequency are low. As a result, the charged potential of the photosensitive member is not uniform, resulting in an abnormal image. Usually, since image quality is often given priority, the AC voltage and frequency to be applied inevitably tend to be set higher.

  These charging conditions are often determined at the initial stage when a new image forming apparatus is developed. Therefore, the vibration and assembly accuracy of the image forming apparatus are often determined in an incomplete state. In order to make the charging potential uniform, the AC voltage and frequency applied to the charging roller are often set to large values, and the oxidative deterioration of the photosensitive member and the charging roller is accelerated.

  It is sufficient if the life of the photoconductor and charging roller is set low and the photoconductor and charging roller are replaced in a short cycle. However, it is necessary to set as gentle charging conditions as possible in order to reduce maintenance costs and replacement costs. There is.

  However, as described above, since it is difficult to accurately see how charging (discharge) occurs, it is only possible to estimate the quality of the charging process by measuring the charging potential of the photoreceptor. The charging potential of the photoconductor can also be measured only in a few limited places. For this reason, the charging conditions are often set high, and the life of the photoconductor and the charging roller has been shortened.

  Also, if the surface of the photoconductor or charging roller is oxidized and deteriorated, the toner component easily adheres to the photoconductor or charging roller, and the adhering material is oxidized by discharge and becomes ionic. This is likely to occur, and blur is likely to occur on the photoconductor, and streaky abnormal images are likely to occur on the charging roller. Therefore, relaxing the charging condition is important for suppressing these abnormal images.

  An object of the present invention is to obtain a uniform charging potential by performing efficient charging, reduce the rate of oxidative deterioration of the photosensitive member and the charging roller, and extend the life of the photosensitive member and the charging roller.

  The present inventors have intensively studied whether there is a simple and accurate method for determining whether or not the charging process is operating well. As a result, in the charging process in which the photosensitive member is charged by applying an AC voltage superimposed with a DC voltage to the charging roller disposed in a non-contact manner with the photosensitive member and the photosensitive member, a part of energy generated by the discharge is Paying attention to the fact that it is high enough to cut the CC bond between organic substances on the charging roller and photoconductor, and if the AC voltage superimposed with the DC voltage is applied for a long time without rotating the photoconductor and the charging roller, It has been found that streaky defects occur in the roller and the photoconductor, and the streaky defects are caused by variations in the distance between the photoconductor and the charging roller and in the discharge caused by variations in the respective electrical characteristics. We found that unevenness can be visualized.

  In view of this, the present inventors have intensively studied how to form a uniform charging potential to the photosensitive member while suppressing the rate of oxidative deterioration of the photosensitive member and the charging roller with gentle charging when the discharge is generated. As a result, if the width of occurrence of a single discharge is made as wide as possible, the discharge will not concentrate locally, and the speed of oxidative degradation of the charging roller and the photoreceptor can be reduced. In addition, if the discharge width is as uniform as possible at each location in the longitudinal direction of the charging roller and the charging roller without being divided, the frequency at which the AC voltage is applied during charging is set lower. In addition, the inventors have found that the charging potential of the photosensitive member can be made uniform, and the speed of oxidative deterioration of the photosensitive member and the charging roller can be reduced, and the present invention has been achieved.

That is, the present invention is, to the charging roller disposed in non-contact with respect to the photosensitive member, a charging condition adjusting method for a charging device which performs charging by applying an AC voltage superimposed with a direct current voltage, a photosensitive member A step of applying an alternating voltage on which the direct current voltage is superimposed for a certain period of time without rotating both of the charging rollers ; and a step of observing a discharge trace generated on the photoconductor. The charging conditions are adjusted so that the average (L) of the width of the discharge trace is 0.9 mm or more and the difference between the maximum and minimum of the discharge trace width is 20% or less of the average discharge trace width. It is a feature .

  If the conditions described in the claims of the present application are satisfied, high-quality image formation is possible, and the replacement frequency of the photosensitive member and the charging roller can be suppressed.

  The method for determining the discharge traces in the image forming area generated on the photoconductor or the charging roller by applying an AC voltage superimposed with the DC voltage for a certain time without rotating both the photoconductor and the charging roller is as follows. Either a forming apparatus or a unit composed only of a photosensitive member and a charging roller may be used, but the voltage applied to the charging roller and the photosensitive member must be that of an actual image forming apparatus. Normally, in an actual image forming apparatus, the electric current flowing in the charging process is controlled in consideration of the electrical characteristics of the charging roller and the photosensitive member due to environmental fluctuations, and the AC voltage applied to the charging roller is changed. There are many. In this case, the application conditions are preferably set in an environment where the image forming apparatus is mainly used (for example, a temperature of 23 ° C. and a humidity of 55%).

  Usually, the voltage applied to the charging roller is a DC voltage of 300 to 900 (-V), preferably 400 to 800 (-V), and more preferably 450 to 700 (-V). If the voltage applied to the charging roller is less than 300 (-V), the charging potential of the photosensitive member is low, and a sufficient light attenuation curve of the photosensitive member cannot be obtained. When the voltage applied to the charging roller is greater than 900 (-V), when the film thickness of the photoconductor becomes thin, the carrier in the developer adheres to the photoconductor and generates an abnormal image of the spot, An abnormal image of dirt is likely to occur, which is not preferable. The AC voltage applied to the charging roller is 1500 V to 3000 V, preferably 1600 V to 2700 V, more preferably 1700 V to 2500 V as peak to peak. When the AC voltage applied to the charging roller is less than 1600 V, the charged potential unevenness of the photoconductor is likely to occur. When the voltage exceeds 3000 V, the photoconductor and the charging roller are oxidized and deteriorated due to discharge at the closest location. The speed is extremely high, and the life of the photoconductor and the charging roller is shortened. The frequency of the AC voltage applied to the charging roller is appropriately determined depending on the linear velocity of the photosensitive member and the resolution of the image to be formed, but is 300 Hz to 4000 Hz, preferably 500 Hz to 3000 Hz, more preferably 600 Hz to 2500 Hz. It is. If the frequency of the AC voltage applied to the charging roller is less than 300 Hz, uneven charging of the photoconductor tends to occur, and an abnormal image of horizontal stripes tends to occur, which is not preferable. If the frequency of the AC voltage applied to the charging roller is higher than 4000 Hz, the speed of oxidation deterioration of the photoconductor and the charging roller becomes extremely fast, and the life of the photoconductor and the charging roller is shortened, which is not preferable.

  In order to observe the discharge trace generated on the photosensitive member, the time applied to the charging roller may be any time as long as the discharge trace can be observed. However, the discharge trace becomes earlier as the frequency f (Hz) of the alternating current applied to the charging increases. In order to appear, f / 1000 to f / 10 minutes, preferably f / 500 to f / 20 minutes, and more preferably f / 250 to f / 25 minutes. If the application time is less than f / 1000 minutes, the discharge trace is unclear, so it is difficult to accurately determine the width of the discharge trace, and if it is longer than f / 10 minutes, the photoreceptor or the charging roller may be damaged. In particular, in the case of a photoreceptor or a charging roller having a surface layer, when the surface layer disappears due to charging, the rate of oxidative deterioration below the surface layer is often increased, which is dangerous and is not preferable.

A schematic diagram of discharge traces generated on the photoreceptor in the present invention is shown in FIG. The discharge trace can be observed with an optical microscope, an electron microscope or the like at a magnification of about 5 to 50 times.
In the present invention, there is substantially one discharge mark generated on the photoreceptor. If the distance between the photosensitive member and the charging roller is too close, there is a place where no discharge is generated at the center of the discharge trace, and therefore there are two discharge traces. That is, when there is only one discharge mark, the photosensitive member and the charging roller are completely separated from each other, and the width of the discharge can be increased in one cycle of the AC voltage applied to the charging roller. Therefore, even if the frequency f (Hz) of the AC voltage applied to the charging roller is set low, it is possible to make the charging potential of the photosensitive member uniform. In the present invention, the width of the discharge trace is preferably as wide as possible, and the average (L) of the width of the discharge trace is 0.9 mm or more, preferably 1.0 mm or more, more preferably 1.1 mm to 2 mm. If the average width of the discharge trace is less than 0.9 mm, it is necessary to set the frequency of the AC voltage applied to the charging roller to be higher in order to make the charging potential of the photosensitive member uniform. This is not preferable because the speed of oxidative deterioration is increased and the photosensitive member and the charging roller must be replaced at an early stage. As a method for increasing the width of the discharge mark, it is conceivable to increase the diameter of the photoreceptor and / or the charging roller. When the voltage to be applied to the charging roller is determined, the discharge occurs when the distance between the photosensitive member and the charging roller is within a certain range. If the diameter of the photosensitive member and / or the charging roller is increased, the region where the distance between the photosensitive member and the charging roller is within a certain range is increased, and thus the width of the discharge trace can be increased. However, if the diameter of the charging roller and / or the photosensitive member is too large, the apparatus becomes large, and unless the accuracy of assembly is increased, the width in which discharge occurs easily changes depending on the location, and the variation in the width of the discharge mark increases. End up. Therefore, the outer diameter of the charging roller is suitably 9 mm to 25 mm, preferably 10 mm to 20 mm.

  The variation in the width of the discharge trace is also extremely important, and the difference between the upper limit and the lower limit of the width of the discharge trace is 20% or less, preferably 18% or less, more preferably 12% or less of the average of the width of the discharge trace. If the difference between the upper limit and the lower limit of the width of the discharge mark is greater than 20%, it is necessary to set the frequency of the alternating voltage applied to the charging roller higher in order to make the charging potential of the photosensitive member uniform. The speed of oxidation deterioration of the charging roller is increased, and the photosensitive member and the charging roller must be replaced at an early stage, which is not preferable. Variations in the width of the discharge mark are due to variations in the discharge width caused by vibration of the photosensitive member and / or charging roller, insufficient assembly accuracy of the photosensitive member and / or charging roller, and variations in electrical characteristics or shape of the photosensitive member and / or charging roller. It is. In the conventional method, the width of the discharge was not known, so the frequency of the alternating current applied to the charging potential was set higher, and the speed of the oxidative deterioration of the photoconductor and the charging roller was increased, so that In addition, the photoconductor and charging roller had to be replaced. In the present invention, the place where the discharge occurs can be specified by the discharge trace, so that the frequency of the alternating current applied to the charging potential can be set to an appropriate value, and the replacement interval of the photosensitive member and the charging roller can be set. Can be greatly extended.

In the present invention, when the linear velocity of the photoconductor is v (mm / sec) and the average of the width of the discharge mark generated on the photoconductor is L (mm), ideally f ≧ v / L
If this is the case, the charged potential of the photoreceptor is constant. Actually, in the discharge of one cycle of the AC voltage applied to the charging roller, since the charging potential of the width of the discharge mark varies, the frequency is 17.0 × v / L ≧ f ≧ 4.0 × v / L, Preferably 15.0 × v / L ≧ f ≧ 4.5 × v / L, more preferably 13.0 × v / L ≧ f ≧ 5.0 × v / L. If the frequency is less than 4.0 × v / L, uniformity of the charged potential of the photoreceptor cannot be obtained, and a high quality image can be obtained particularly in an image forming apparatus having a resolution of 1000 dpi, preferably 1200 dpi or more. It is not preferable. If the frequency is higher than 15.0 × v / L, the speed of the oxidative degradation of the photoconductor and the charging roller is high, and it is necessary to replace the photoconductor and the charging roller at an early stage, which is not preferable.

  In the present invention, an image forming apparatus having high image quality and high reliability can be provided regardless of the linear velocity of the photosensitive member. In particular, the linear velocity is 150 mm / second or more, preferably 220 mm / second. More than 1 second, more preferably at 280 mm / second to 800 mm / second, it is possible to slow down the oxidative deterioration of the photosensitive member and the charging roller, and to extend the life of the photosensitive member and the charging roller. . This is because the present invention performs efficient charging. In the conventional charging process, the place where the strong discharge and the weak place are mixed, so in order to make the charged potential of the photoreceptor uniform, the charging is performed based on the place where the discharge is weak. I decided the conditions. Even in the conventional charging process, when the linear velocity of the photosensitive member is low, the influence is small, but when the linear velocity of the photosensitive member is increased, the variation in the charging potential of the photosensitive member is increased, so that the charging condition is strengthened. The speed of oxidation deterioration of the photoconductor and the charging roller has increased, and the photoconductor and the charging roller had to be replaced at an early stage.

  In the photoreceptor used in the image forming apparatus of the present invention, a photosensitive layer is provided on a conductive support. The photosensitive layer is composed of a single layer type in which a charge generation material and a charge transport material are mixed, a forward layer type in which a charge transport layer is provided on the charge generation layer, or a charge generation layer on the charge transport layer. There is a reverse layer type provided. A protective layer can also be provided on the photosensitive layer. An undercoat layer may be provided between the photosensitive layer and the conductive support. If necessary, an appropriate amount of a plasticizer, an antioxidant, a leveling agent and the like can be added to each layer.

Examples of the conductive support for the photoreceptor include those having a volume resistance of 10 ¹⁰ Ωcm or less, for example, metals such as aluminum, nickel, chromium, nichrome, copper, gold, silver, platinum, tin oxide, indium oxide, etc. A metal or oxide film, or a film or cylindrical plastic or paper coated by vapor deposition or sputtering, or a plate made of aluminum, aluminum alloy, nickel, stainless steel, etc. After forming a blank, a tube that has been surface-treated by cutting, superfinishing, polishing, or the like can be used. As the drum-shaped support, those having a diameter of 20 mm to 150 mm, preferably 24 mm to 100 mm, and more preferably 28 mm to 70 mm can be used. If the diameter of the drum-shaped support is less than 20 mm, it is physically difficult to arrange means for charging, exposing, developing, transferring, and cleaning steps around the drum, and the diameter of the drum-shaped support is more than 150 mm. If it is large, the image forming apparatus becomes large, which is not preferable. In particular, when the image forming apparatus is a tandem type, it is necessary to mount a plurality of photoconductors, and thus the diameter is preferably 70 mm or less, and preferably 60 mm or less. Further, endless nickel belts and endless stainless steel belts disclosed in JP-A-52-36016 can also be used as the conductive support.

  As the undercoat layer of the photosensitive member used in the image forming apparatus of the present invention, a resin or a material mainly composed of a white pigment and a resin, and a metal oxide obtained by chemically or electrochemically oxidizing the surface of a conductive substrate Examples of the film include a white pigment and a resin as main components. Examples of white pigments include metal oxides such as titanium oxide, aluminum oxide, zirconium oxide, and zinc oxide. Among them, it is most preferable to contain titanium oxide that is excellent in preventing charge injection from a conductive substrate. Examples of the resin used for the undercoat layer include thermoplastic resins such as polyamide, polyvinyl alcohol, casein, and methylcellulose; thermosetting resins such as acrylic, phenol, melamine, alkyd, unsaturated polyester, and epoxy; Various mixtures can be exemplified.

  Examples of the charge generating substance for the photoreceptor used in the image forming apparatus of the present invention include azo pigments such as monoazo pigments, bisazo pigments, trisazo pigments, and tetrakisazo pigments, triarylmethane dyes, thiazine dyes, Oxazine dyes, xanthene dyes, cyanine dyes, styryl dyes, pyrylium dyes, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, bisbenzimidazole pigments, indanthrone pigments, squarylium Organic pigments and dyes such as pigments, phthalocyanine pigments, inorganic materials such as selenium, selenium-arsenic, selenium-tellurium, cadmium sulfide, zinc oxide, titanium oxide, amorphous silicon, etc. can be used, and charge generating substances Can be used alone or in combination.

  Examples of the charge transport material for the photoreceptor used in the image forming apparatus of the present invention include anthracene derivatives, pyrene derivatives, carbazole derivatives, tetrazole derivatives, metallocene derivatives, phenothiazine derivatives, pyrazoline compounds, hydrazone compounds, styryl compounds, styrylhydrazone compounds. , Enamine compounds, butadiene compounds, distyryl compounds, oxazole compounds, oxadiazole compounds, thiazole compounds, imidazole compounds, triphenylamine derivatives, phenylenediamine derivatives, aminostilbene derivatives, triphenylmethane derivatives, etc. Can be used.

  The binder resin used for forming the photosensitive layer of the charge generation layer and the charge transport layer is electrically insulating, and is a known thermoplastic resin, thermosetting resin, photocurable resin, and photoconductive material. Suitable binder resins include, for example, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, Ethylene-vinyl acetate copolymer, polyvinyl butyral, polyvinyl acetal, polyester, phenoxy resin, (meth) acrylic resin, polystyrene, polycarbonate, polyarylate, thermoplastic resin such as polysulfone, polyethersulfone, ABS resin, phenol resin , Epoxy resin, urethane resin, melamine resin, isocyanate resin, alkyd tree In addition, a thermosetting resin such as a silicone resin and a thermosetting acrylic resin, a photoconductive resin such as polyvinyl carbazole, polyvinyl anthracene, and polyvinyl pyrene, or a mixture of various types of binder resins can be given. However, the present invention is not particularly limited to these.

As antioxidant, the following are used, for example.
[Monophenol compound]
2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, stearyl-β- (3,5-di-t-butyl-4 -Hydroxyphenyl) propionate, 3-t-butyl-4-hydroxynisol, etc. [bisphenol compounds]
2,2′-methylene-bis- (4-methyl-6-tert-butylphenol), 2,2′-methylene-bis- (4-ethyl-6-tert-butylphenol), 4,4′-thiobis- ( 3-methyl-6-tert-butylphenol), 4,4′-butylidenebis- (3-methyl-6-tert-butylphenol), etc. [polymeric phenol compound]
1,1,3-tris- (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t- Butyl-4-hydroxybenzyl) benzene, tetrakis- [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane, bis [3,3′-bis (4 ′) -Hydroxy-3'-t-butylphenyl) butyric acid] glycol ester, tocophenols, etc. [paraphenylenediamines]
N-phenyl-N'-isopropyl-p-phenylenediamine, N, N'-di-sec-butyl-p-phenylenediamine, N-phenyl-N-sec-butyl-p-phenylenediamine, N, N'- Di-isopropyl-p-phenylenediamine, N, N′-dimethyl-N, N′-di-t-butyl-p-phenylenediamine, etc. [hydroquinones]
2,5-di-t-octylhydroquinone, 2,6-didodecylhydroquinone, 2-dodecylhydroquinone, 2-dodecyl-5-chlorohydroquinone, 2-t-octyl-5-methylhydroquinone, 2- (2-octadecenyl) ) -5-Methylhydroquinone etc. [Organic sulfur compounds]
Dilauryl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, ditetradecyl-3,3′-thiodipropionate, etc. [Organic phosphorus compounds]
Triphenylphosphine, tri (nonylphenyl) phosphine, tri (dinonylphenyl) phosphine, tricresylphosphine, tri (2,4-dibutylphenoxy) phosphine and the like.

  As the plasticizer, those used as plasticizers for general resins such as dibutyl phthalate and dioctyl phthalate can be used as they are, and the amount used is about 0 to 30 parts by weight with respect to 100 parts by weight of the binder resin. Is appropriate.

  A leveling agent may be added to the charge transport layer. As the leveling agent, silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, and polymers or oligomers having a perfluoroalkyl group in the chain are used, and the amount used is 0 to 100 parts by weight of the binder resin. One part by weight is appropriate.

  The protective layer is a layer in which fine particles of metal or metal oxide are dispersed in a binder resin. As the binder resin, a resin that is transparent to visible and infrared light and excellent in electrical insulation, mechanical strength, and adhesiveness is desirable. As the binder resin of the protective layer, ABS resin, ACS resin, olefin-vinyl monomer copolymer, chlorinated polyether, allyl resin, phenol resin, polyacetal, polyamide, polyamideimide, polyacrylate, polyallylsulfone, polybutylene, Polybutylene terephthalate, polycarbonate, polyethersulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic resin, polymethylbenten, polypropylene, polyphenylene oxide, polysulfone, polystyrene, AS resin, butadiene-styrene copolymer, polyurethane, polyvinyl chloride, poly Examples of the resin include vinylidene chloride and epoxy resin. Examples of the metal oxide include titanium oxide, tin oxide, potassium titanate, TiO, TiN, zinc oxide, indium oxide, and antimony oxide. In addition to the protective layer, fluorine resins such as polytetrafluoroethylene, silicone resins, and those obtained by dispersing other inorganic materials in these resins can be added for the purpose of improving wear resistance. As a method for forming the protective layer, a normal coating method is employed. The thickness of the protective layer is suitably about 0.1 μm to 10 μm.

  Examples of the solvent used for producing the photoreceptor include chlorinated solvents such as dichloromethane, tetrahydrofuran, dioxane, toluene, cyclohexanone, methyl ethyl ketone, acetone and the like.

  At both ends of a photosensitive member provided with a photosensitive layer on a drum-shaped conductive support, flanges are usually provided for supporting the photosensitive member and transmitting rotation from the main body driving device. Engineering plastics such as polyamide, polyacetal, polyethylene terephthalate, polyphenylene sulfide, polyether ketone, liquid crystal polymer, polycarbonate, polyphenylene ether, polyarylate, polysulfone, polyethersulfone, polyetherimide, polyamideimide, etc. with excellent mechanical strength In order to control mechanical strength, rigidity, conductivity, etc., fibers such as glass fiber, carbon fiber, fillers such as carbon, talc, kaolin, calcium carbonate, alumina, silica, and various additives are used. Used by mixing. These flanges are press-fitted into a drum-like conductive support and fixed with an adhesive or the like.

  In the present invention, high-quality image formation is possible in both monochrome image formation and color image formation, but the effect is particularly high in color image formation that requires high-quality image formation. While doing so, the life of the photoreceptor and the charging roller can be greatly extended. When the present invention is capable of forming a color image, a single photoconductor is used, and after developing the toner of each color on the photoconductor, the toner image on the photoconductor of each color is sequentially transferred to the intermediate transfer member or the image carrier. A method for forming an image, a method in which a photosensitive member is used for the number of toner colors, each color toner is developed on a separate photosensitive member, and transferred to an intermediate transfer member or an image carrier (tandem type or the like). ) Both have excellent performance. In the tandem type, it is necessary to take a charging step with a charging roller in order to suppress the generation of an oxidizing gas such as ozone accompanying charging, but the charging step used in the present invention has gentle charging conditions. The amount of oxidizing gas generated is particularly small. Therefore, the present invention is not only capable of forming a high-quality and highly reliable image, but is also environmentally friendly.

The charging condition adjusting method according to the present invention will be described in more detail with reference to the drawings.
FIG. 2 schematically shows an image forming apparatus according to the present invention. The image forming apparatus shown here is configured as a copying machine, a printer, a facsimile, or a multifunction machine having at least two of these functions. A photoreceptor 1 as an example of a member to be charged is disposed in a main body housing (not shown), and the photoreceptor 1 is configured by laminating a photosensitive layer 3 on the outer peripheral surface of a conductive base 2 on a drum. Yes. It is also possible to use a belt-like photoreceptor that is wound and driven around a plurality of rollers, or a drum-like or belt-like photoreceptor made of a dielectric. In the present embodiment, at least the photosensitive member 1 and the charging device 5 constitute a process cartridge unit, and a developing device, a cleaning unit, and a charge removal device can be further added to constitute a process cartridge. When referred to as a process cartridge, the cartridge unit alone can be a process cartridge, and there can be various variations such as a charging device, a photoreceptor, a developing device, a charging device, a photoreceptor, a developing device, and a cleaning device.

  During the image forming operation, the photosensitive member 1 is rotationally driven clockwise in FIG. 2, and the surface thereof moves in the direction of arrow A. At this time, the surface of the photosensitive member is irradiated with light from the static elimination lamp 4, the surface is initialized, and then the surface of the photosensitive member is charged to a predetermined polarity by the charging device 5 (the charging device 5 will be described in detail later). . The surface of the photosensitive member charged by the charging device 5 is irradiated with light-modulated laser light emitted from a laser writing unit 6 which is an example of an exposure device, thereby forming an electrostatic latent image on the surface of the photosensitive member. The Next, when the electrostatic latent image passes through the developing device 7, it is visualized as a toner image by toner charged to a predetermined polarity.

  On the other hand, a transfer material P (paper) is fed between the photoconductor 1 and the transfer device 8 opposed to the photoconductor 1 at a predetermined timing. At this time, a toner image formed on the photoconductor is transferred onto the transfer material P. Is electrostatically transferred to. The transfer material P to which the toner image has been transferred subsequently passes between the fixing roller 10 and the pressure roller 11 of the fixing device 9, and the toner image is fixed on the transfer material by the action of heat and pressure. The The transfer residual toner that is not transferred to the transfer material and remains on the surface of the photoreceptor is removed by the cleaning device 12.

  The charging device 5 includes a charging roller 13 disposed to face a surface of a charged object to be moved, in the illustrated example, the surface of the photosensitive member 1, and a power source 14 that applies a voltage to the charging roller 13. A voltage is applied to the charging roller 13 by the power source 14 to generate a discharge between the charging roller 13 and the surface of the photoconductor to charge the surface of the photoconductor with a predetermined polarity.

  The charging roller 13 is preferably configured to have a polymer layer and a surface layer on a conductive support as a layer configuration. The conductive support functions as an electrode and a support member for the charging roller. For example, a metal or alloy such as aluminum, copper alloy, stainless steel, iron plated with chromium, nickel, or the like, resin of a conductive agent It is made of a conductive material such as.

The polymer layer is preferably a conductive layer having a resistance of 10 ⁶ Ωcm to 10 ⁹ Ωcm, and a polymer material mixed with a conductive material to adjust the resistance is used. As the polymer of the polymer layer of the charging roller, styrenic resins such as polyester-based, olefin-based thermoplastic elastomer, polystyrene, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, etc. Thermoplastic resin, isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, urethane rubber, silicone rubber, fluoro rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide- Allyl glycidyl ether copolymer rubber, ethylene-propylene-diene terpolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber, natural rubber, etc. And rubber material obtained by blending thereof. Among the rubber materials, silicone rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, acrylonitrile-butadiene copolymer rubber and blended rubber thereof are preferably used. These rubber materials may be foamed or non-foamed.

  As the conductive agent, an electronic conductive agent or an ionic conductive agent is used. Examples of electronic conductive agents include carbon blacks such as ketjen black and acetylene black; pyrolytic carbon, graphite; various conductive metals or alloys such as aluminum, copper, nickel, and stainless steel; tin oxide, indium oxide, titanium oxide Examples thereof include various conductive metal oxides such as tin oxide-antimony oxide solid solution and tin oxide-indium oxide solid solution; those obtained by conducting the surface of an insulating material; Examples of ionic conductive agents include perchlorates and chlorates such as tetraethylammonium and lauryltrimethylammonium; alkali metals such as lithium and magnesium; perchlorates and chlorates of alkaline earth metals Can be mentioned. These conductive agents may be used alone or in combination of two or more. Moreover, the addition amount is not particularly limited, but in the case of the electronic conductive agent, it is preferably in the range of 1 to 30 parts by mass with respect to 100 parts by mass of the polymer, and in the range of 15 to 25 parts by mass. More preferably. On the other hand, in the case of the ionic conductive agent, it is preferably in the range of 0.1 to 5.0 parts by mass, and in the range of 0.5 to 3.0 parts by mass with respect to 100 parts by mass of the polymer. Is more preferable.

  The polymer material constituting the surface layer is not particularly limited as long as the dynamic ultra-small hardness on the surface of the charging roller is 0.04 or more and 0.5 or less, but polyamide, polyurethane, polyvinylidene fluoride, tetrafluoroethylene Copolymer, polyester, polyimide, silicone resin, acrylic resin, polyvinyl butyral, ethylene tetrafluoroethylene copolymer, melamine resin, fluoro rubber, epoxy resin, polycarbonate, polyvinyl alcohol, cellulose, polyvinylidene chloride, polyvinyl chloride, polyethylene And ethylene vinyl acetate copolymer. Among these, polyamide, polyvinylidene fluoride, tetrafluoroethylene copolymer, polyester, and polyimide are preferably used from the viewpoint of releasability with toner and the like. The above polymer materials may be used alone or in combination of two or more. Further, the number average molecular weight of the polymer material is preferably in the range of 1000 to 100,000, and more preferably in the range of 10,000 to 50,000.

  The surface layer is formed as a composition by mixing the polymer material with the conductive agent used in the conductive elastic layer and various fine particles. As the fine particles, metal oxides such as silicon oxide, aluminum oxide, and barium titanate and composite metal oxides, and polymer fine powders such as tetrafluoroethylene and vinylidene fluoride are used alone or in combination. It is not limited to.

  The charging roller 13 shown in FIG. 2 is opposed to the surface of the photoreceptor with a small gap G of, for example, 25 μm to 150 μm, preferably 30 μm to 120 μm, more preferably 40 μm to 100 μm. If the minute gap G is less than 25 μm, there may be a place where no discharge occurs in a portion close to the charging roller and the photosensitive member when the dimensional accuracy and assembly accuracy of the charging roller 13 and the photosensitive member are low. Therefore, it is not preferable. Further, if the minute gap G exceeds 150 μm, it is necessary to increase the AC voltage applied to the charging roller in order to cause discharge, and if it is too large, the amount of ozone generated increases. It is not preferable.

  FIG. 3 shows an example of a configuration for placing the charging roller 13 on the surface of the photosensitive member with a minute gap G therebetween. The charging roller 13 shown here has a spacer made of a tape 20 attached to each end region in the longitudinal direction. The tape 20 comes into contact with the surface of the photosensitive member so that the charging roller 13 is brought into contact with the surface of the photosensitive member. On the other hand, the minute gap G is maintained. In addition, a minute gap can be secured using a flange or the like.

  In the present invention, it is very preferable that the photosensitive member, the charging roller, development, and cleaning are integrated into a so-called process cartridge that is handled as a replacement part because the maintainability is remarkably improved.

[Example 1 and Comparative Examples 1 and 2]
An undercoat layer, a charge generation layer, a charge transport layer, and a protective layer were applied in this order on an aluminum drum (conductive support) having a diameter of 30 mm, and then dried, followed by 3.9 μm undercoat layer, 0.15 μm. A photoconductor comprising a charge generation layer, a 22 μm charge transport layer, and a protective layer of about 4.5 μm was prepared. At this time, the coating of the protective layer was performed by a spray method, and the others were performed by a dip coating method. 22.5% by mass of alumina having an average particle size of 0.21 μm was added to the protective layer.

  Three types of charging rollers supplied by charging roller manufacturers as imagio Neo C385 (tandem color image forming device, photosensitive member linear velocity: 185 mm / second, writing light resolution of 600 dpi, manufactured by Ricoh). The charging roller prototype was evaluated. The charging roller was prepared by attaching a conductive rubber mainly composed of epichlorohydrin rubber and conductive carbon to a stainless steel cylinder, and had a rubber hardness (type A) of 64, 76, and 87. The diameter of each charging roller was 11.5 mm. A gap tape having a width of 10 mm and a thickness of 52 μm was attached to a position 13 mm from the end of each charging roller. A charging roller is disposed immediately above the photosensitive member, and the charging roller is pressed against the photosensitive member with a spring, and a frequency of 890 Hz is applied to a DC voltage of −600 V between the photosensitive member and the charging roller under the condition that the photosensitive member and the charging roller are not rotated. An AC voltage with an amplitude of 1050 V was applied for 10 minutes. White streaks of discharge traces were formed on the charging roller and the photoreceptor. When the discharge trace near the center of the photosensitive member was observed, two discharge traces were observed when charged with a charging roller having a rubber hardness of 64, and the width of one discharge trace was 0.49 mm. . The one charged with a charging roller having a rubber hardness of 76 and 87 is one discharge mark, and the width of the discharge mark is 1.32 mm on the average for a charging roller having a rubber hardness of 76, and the width of the discharge mark. The difference between the maximum and minimum was 0.07 mm, the average of 1.17 mm for the charging roller having a rubber hardness of 87, and the difference between the maximum and minimum of the width of the discharge trace was 0.23 mm.

  Replacing the charging roller and photoreceptor with rubber hardness (type A) of 64, 76 and 87 with new ones, charging roller with rubber hardness of 64 to black photoreceptor unit, and charging roller with rubber hardness of 76 to photoreceptor unit for cyan In addition, a charging roller having a rubber hardness of 87 is incorporated in the photosensitive unit for magenta, and charging conditions for applying an AC voltage having a frequency of 890 Hz and an amplitude of 1050 V to a DC voltage of −600 V between the charging roller and the photosensitive member of each photosensitive unit. Then, 50000 black, cyan and magenta halftone images were output as A4 size paper images, as shown in FIG. 4, and then a full-tone halftone image of black, cyan and magenta was output. Black and cyan images are high-quality images, but magenta images have obvious density unevenness (hardness of 7 There In Example 1, hardness 64 and hardness 87 Comparative Examples 1 and 2).

[Example 2 and Comparative Example 3]
Regarding the superposed voltage applied between the photoconductor and the charging roller under the condition that the photoconductor and the charging roller are not rotated, based on the evaluation procedure in the above example, incorporating a charging roller having a rubber hardness of 76 in the magenta photoconductor unit. The AC frequency applied to the charging roller of the black photosensitive unit and the cyan photosensitive unit was 1.3 kHz, and the AC frequency applied to the charging roller of the magenta photosensitive unit was 890 Hz.

  After forming 50,000 sheets of the chart of FIG. 4, the state of the entire halftone image of black, cyan, and magenta was observed. Although cyan and magenta images were high-quality images, streaky abnormal images were seen in black images (hardness 76 cyan was Example 2 and hardness 64 was Comparative Example 3).

[Examples 3 and 4]
A material consisting mainly of ABS resin, carbon and ionic conductive material is laminated on a stainless steel cylinder. A charging roller with a diameter of 13 mm and 22.6 mm is used, and a 60 μm gap tape is pasted at 15 mm from both ends of the charging roller. In addition, based on the evaluation procedure of Example 2 described above, the photoconductor was replaced with a new one and mounted on the used black photoconductor unit and yellow photoconductor unit. Charging rollers having a diameter of 13 mm and a diameter of 22.6 mm were incorporated in the black photoconductor unit and the yellow photoconductor unit, respectively. For the black photosensitive unit between the photosensitive member and the charging roller without rotating the charging roller, the yellow photosensitive member is applied under a charging condition in which an AC voltage having a frequency of 890 Hz and an amplitude of 1200 V is applied to a -600V DC voltage. For the unit, the charging conditions were such that an AC voltage with a frequency of 850 Hz and an amplitude of 1200 V was applied to a DC voltage of -600 V, and the other photoconductor units (cyan, magenta) were charged in the above [Example 2, Comparative Example 3]. Same as roller and charging conditions.

  When one white streak discharge trace generated near the center of the photoreceptor was observed, the width of the discharge trace was 1.21 mm on the average for the black photoreceptor unit, and the difference between the maximum and minimum width of the discharge trace was 0. The average of the yellow photoconductor units was 1.83 mm, and the difference between the maximum and minimum discharge trace widths was 0.08 mm. After forming 50,000 sheets of each color mixed chart, the state of the entire halftone image of black, yellow, cyan and magenta was observed. High quality images were obtained for all the images (black is Example 3 and yellow is Example 4).

[Examples 5 to 8]
Based on the evaluation procedure of [Examples 3 and 4] above, modification was made so that the photosensitive member linear velocity of each photosensitive unit was 222 mm / second and the resolution of the writing light was 1200 dpi. Regarding the superimposed voltage applied between the photoconductor and the charging roller under the condition that the photoconductor unit used in [Examples 3 and 4] is used as it is and the photoconductor and the charging roller are not rotated, the black photoconductor unit is − Under the charging conditions in which an AC voltage having a frequency of 1100 Hz and an amplitude of 1200 V is applied to a DC voltage of 600 V, the yellow photoconductor unit has a charging condition of applying an AC voltage having a frequency of 1000 Hz and an amplitude of 1200 V to a DC voltage of −600 V, and for cyan. The photoconductor unit has a charging condition in which an AC voltage having a frequency of 1700 Hz and an amplitude of 1050 V is applied to a DC voltage of −600 V, and the magenta photoconductor unit applies an AC voltage having a frequency of 2000 Hz and an amplitude of 1050 V to a DC voltage of −600 V. Charging conditions were used. After a total of 70,000 images of each color mixed chart were formed, black, yellow, cyan, and magenta full-tone images were output. As a result, a high-quality image was obtained.

It is a schematic diagram of the discharge trace which arises on a photoreceptor. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. It is a figure explaining the micro gap of a charging roller and a photoreceptor. It is explanatory drawing of the hybrid image at the time of performing image evaluation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 4 Static elimination lamp 5 Charging apparatus 6 Laser writing unit 7 Developing apparatus 8 Transfer apparatus 9 Fixing apparatus 12 Cleaning apparatus

Claims (8)

A charging condition adjustment method for a charging device that performs charging by applying an AC voltage superimposed with a DC voltage to a charging roller arranged in non-contact with the photosensitive member ,
Applying an AC voltage on which the DC voltage is superimposed for a certain period of time without rotating both the photoconductor and the charging roller ;
Observing discharge traces generated on the photoreceptor,
Wherein a discharge crater is one streak, charging the average width of the discharge trace (L) is 0.9mm or more, as the difference between the maximum and minimum discharge crater width is less than 20% of the average discharge trace width A charging condition adjusting method, characterized by adjusting conditions . 2. The charging condition adjusting method according to claim 1, wherein the parameter relating to the charging condition is a hardness of the charging roller. 3. The charging condition adjusting method according to claim 1 or 2, wherein the parameter relating to the charging condition is a frequency of the AC voltage. In charging condition adjusting method of claim 3, wherein the AC voltage of the frequency of the superimposed voltage applied to the charging roller (fHz), average width of the discharge trace (L mm), the line of the photosensitive member at the time of image formation speed (vmm / sec.) for and 17 × v / L ≧ f ≧ 4 × v / L
A charging condition adjusting method, wherein the charging condition is adjusted so that 5. The charging condition adjusting method according to claim 1, wherein the parameter relating to the charging condition is a size of a gap formed between the charging roller and the photosensitive member. Condition adjustment method. An image forming apparatus comprising a photoconductor for forming a latent image and a charging device for charging the photoconductor, using the charging condition adjusting method according to any one of claims 1 to 5, An image forming apparatus, wherein a charging condition of the charging device is adjusted . The image forming apparatus according to claim 6, images forming device you wherein the imageable highest resolution is equal to or greater than 1000dpi. A process cartridge comprising a photosensitive member on which a latent image is formed and a charging device for charging the photosensitive member, wherein the charging condition adjusting method according to any one of claims 1 to 5 is used. A process cartridge in which charging conditions of a charging device are adjusted .

Images